xref: /openbmc/linux/net/ceph/ceph_hash.c (revision cc8bbe1a)
1 
2 #include <linux/ceph/types.h>
3 #include <linux/module.h>
4 
5 /*
6  * Robert Jenkin's hash function.
7  * http://burtleburtle.net/bob/hash/evahash.html
8  * This is in the public domain.
9  */
10 #define mix(a, b, c)						\
11 	do {							\
12 		a = a - b;  a = a - c;  a = a ^ (c >> 13);	\
13 		b = b - c;  b = b - a;  b = b ^ (a << 8);	\
14 		c = c - a;  c = c - b;  c = c ^ (b >> 13);	\
15 		a = a - b;  a = a - c;  a = a ^ (c >> 12);	\
16 		b = b - c;  b = b - a;  b = b ^ (a << 16);	\
17 		c = c - a;  c = c - b;  c = c ^ (b >> 5);	\
18 		a = a - b;  a = a - c;  a = a ^ (c >> 3);	\
19 		b = b - c;  b = b - a;  b = b ^ (a << 10);	\
20 		c = c - a;  c = c - b;  c = c ^ (b >> 15);	\
21 	} while (0)
22 
23 unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)
24 {
25 	const unsigned char *k = (const unsigned char *)str;
26 	__u32 a, b, c;  /* the internal state */
27 	__u32 len;      /* how many key bytes still need mixing */
28 
29 	/* Set up the internal state */
30 	len = length;
31 	a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
32 	b = a;
33 	c = 0;               /* variable initialization of internal state */
34 
35 	/* handle most of the key */
36 	while (len >= 12) {
37 		a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
38 			 ((__u32)k[3] << 24));
39 		b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
40 			 ((__u32)k[7] << 24));
41 		c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
42 			 ((__u32)k[11] << 24));
43 		mix(a, b, c);
44 		k = k + 12;
45 		len = len - 12;
46 	}
47 
48 	/* handle the last 11 bytes */
49 	c = c + length;
50 	switch (len) {            /* all the case statements fall through */
51 	case 11:
52 		c = c + ((__u32)k[10] << 24);
53 	case 10:
54 		c = c + ((__u32)k[9] << 16);
55 	case 9:
56 		c = c + ((__u32)k[8] << 8);
57 		/* the first byte of c is reserved for the length */
58 	case 8:
59 		b = b + ((__u32)k[7] << 24);
60 	case 7:
61 		b = b + ((__u32)k[6] << 16);
62 	case 6:
63 		b = b + ((__u32)k[5] << 8);
64 	case 5:
65 		b = b + k[4];
66 	case 4:
67 		a = a + ((__u32)k[3] << 24);
68 	case 3:
69 		a = a + ((__u32)k[2] << 16);
70 	case 2:
71 		a = a + ((__u32)k[1] << 8);
72 	case 1:
73 		a = a + k[0];
74 		/* case 0: nothing left to add */
75 	}
76 	mix(a, b, c);
77 
78 	return c;
79 }
80 
81 /*
82  * linux dcache hash
83  */
84 unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
85 {
86 	unsigned long hash = 0;
87 	unsigned char c;
88 
89 	while (length--) {
90 		c = *str++;
91 		hash = (hash + (c << 4) + (c >> 4)) * 11;
92 	}
93 	return hash;
94 }
95 
96 
97 unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
98 {
99 	switch (type) {
100 	case CEPH_STR_HASH_LINUX:
101 		return ceph_str_hash_linux(s, len);
102 	case CEPH_STR_HASH_RJENKINS:
103 		return ceph_str_hash_rjenkins(s, len);
104 	default:
105 		return -1;
106 	}
107 }
108 EXPORT_SYMBOL(ceph_str_hash);
109 
110 const char *ceph_str_hash_name(int type)
111 {
112 	switch (type) {
113 	case CEPH_STR_HASH_LINUX:
114 		return "linux";
115 	case CEPH_STR_HASH_RJENKINS:
116 		return "rjenkins";
117 	default:
118 		return "unknown";
119 	}
120 }
121 EXPORT_SYMBOL(ceph_str_hash_name);
122